Melt butter or coconut oil in a large pan and add chopped mushrooms and onion.
Saute until translucent and cooked.
Add garlic and saute an additional 2 minutes.
Sprinkle with salt, pepper, and arrowroot and stir.
Add broth and simmer about 10 minutes until it starts to thicken.
Add cream and sour cream and stir in until smooth.
Serve as a soup or use as cream of mushroom soup in recipes.
Notes
Time-saving tip: Make several batches at once and freeze or make a couple days before Thanksgiving and store in the refrigerator. (Here's how to remedy any slight curdling that may occur!)